Increasing survival from sudden cardiac arrest caused by ischemia and infarction, an extremely health problem, requires better understanding of the mechanisms both of the arrhythmias causing it and of the problems encountered during resuscitation attempts. This program project application proposes to use electrical and optical and optical mapping techniques in animals to obtain this information. Project 1 (Chronic monitoring of ischemic models of sudden death) will telemeter from chronically instrumented animals and use of electrical mapping to understand how, when, and why sudden death occurs with ischemia and infarction. Project 2 (Mechanism of VF maintenance in ischemia and infarction) will use optical and electrical mapping to quantify the mechanisms maintaining VF. Project 3 (Purkinje-myocardial reentry in ischemia and infraction) will use electrical mapping to investigate the role of Purkinje fibers in initiating arrhythmias. Project 4 (Defibrillation mechanisms during ischemic arrhythmias) will use electrical mapping to determine the mechanisms for the elevated defibrillation and high incidence of refibrillation in ischemia during resuscitation. Project 5 (Electrical therapy for pulseless electrical activity) will use electrical and optimal mapping to study how new electrical therapies eradicate pulseless electrical activity during resuscitation. Core A (Administration) will administrate and provide biostatistical and manuscript preparation support for the project. Core B (Instrumentation and Software) will provide and software support. Core C (Animal models and pathology) will insure optimal animal care and pathological examination.